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A Northumberland Alpine Gardener's Diary

This entry: 12 May 2008 by John Richards

Northumberland Diary. Entry 74.

Rhodo fest, and plague

We have been away in the gracious city of Edinburgh for the last five days, enjoying the hospitality of the truly excellent 25th Jubilee celebrations of the Scottish Rhododendron Society, the 2008 International Rhododendron Conference, held at the Royal Botanic Gardens. The weather was glorious, almost throughout, and the gardens were on top form. As I have said before, this is not the best rhodo flowering year by a long way, but the May plants have performed better than those that bloom in April and there was a lot to see.

Nevertheless, one of the main themes of the Conference was the grim message of the rapid spread of so-called 'Sudden Oak Death' (Phytophthora ramorum and P. kernoviae) which despite its name actually infects many woody plants, rhododendrons more severely than any others, but also camellias, magnolias, viburnums, drimys and most of the other woody treasures of our great 'Atlantic' gardens. The disease is water-borne, not least on wet feet, and all great gardens now have 'foot and mouth disease type disinfectant mats to tread upon in an attempt to halt the disease. Curiously, Drimys winteri is the most infectious of all hosts. The disease seems to be spreading fastest in warm wet conditions, especially in south-west England, and in some gardens there up to 70% of the rhodos have already been removed in an attempt to slow contagion. Foliage and then whole stems, collapse very rapidly, often leading to total death of the plant in months. At an early stage, brown stains angle up the leaf mid-rib in a characteristic manner. All infected material should be burnt immediately, avoiding contagion by water whereever possible.

Luckily, we should be less susceptible in north-east England, and I have not seen signs of the disease here yet, but it is now appearing in some gardens in western Scotland.

One of the best rhodos here at the moment is that wonderful cross between Rh. forrestii and Rh. sanguineum ssp. didymum, 'Carmen'.

Rhodo fest, and plague

Trilliums
Trilliums are at their best here now (Edinburgh was well ahead of us and most of theirs were finished). Here is a mixture with the very vigorous form of T. kurabayashii we grow, and T. grandiflorum 'Roseum', followed by T. grandiflorum growing in rather too close association with the giant woodland Corydalis nobilis.

Trilliums

One of my favourite ground-covers is the Chinese Golden Saxifrage, Chrysoplenium davidianum. This is similar to the rarer and showier of the two British native species, C. alternifolium, but given a shady humid spot is far more vigorous. It seems common in Scottish gardens, but scarce further south, so perhaps it enjoys our cool, subatlantic conditions.

Wonderful omphs

For my money (and if you are lucky to find one, it takes a bit!), there is no more exotic, wonderful, exciting genus than the small group of eastern Himalayan Primulaceae called Omphalogramma. I take virtually no credit whatever for the next photo, because at the Harrogate Show three weeks ago I was delighted to see that Terry and Kath of the Edrom Nursery were selling well-budded plants under the label O. forrestii. The plant I bought has since flowered (and the flower dropped while we were away) but I was first able to capture some of its beauty. O. forrestii is probably synonymous with O. tibeticum and both are part of the O. souliei complex. It seems mean to cavil about such a fabulous thing, but it seems more closely related to O. vincaeiflorum, another very beautiful plant. Since then mirabile dictu, it seems that the plant of O. delavayi that I grew from seed nearly a decade ago is also going to flower, and you can be sure I shall post it when the flower opens!

Wonderful omphs

Much less exotic, but from the same part of the world is that most tractable of 'nivalid' primulas (section Crystallophlomis), P. chionantha. When we visited Saville Garden a few weeks ago I was delighted to find strong plants with both white and purple (subsp. sinopurpurea) coloured flowers for sale and I chose a pin flowered form of one and a thrum of the other. I have since crossed these so that I can raise seedlings in both colours.

Staying with 'Nivalid' primulas, I promised some months ago that I would show some pictures from the Botanic Garden at Newcastle that I help to run with the keen participation of ten or so volunteers (do get in touch if you live in the North-East of England and would like to join us!). I tend to plant 'spare' seedlings there, and in some cases these have done better than in my own garden.

Until last year, the Chinese P. limbata was a little known species that may never have been in cultivation. It is the most widespread of a complex that also includes P. optata, P. longipetiolata which I found last year on the Zheduo Pass above Kangding, the little-known P. farreriana, and the glorious P. melanops. Amongst these, only P. limbata has the very clear line of meal around the outside of the leaf underside. Josef Jurasek collected seed of this in 2006 and 2007. The young seedlings showed the white band ('limbata' means 'banded') very clearly, so it was a puzzle when the plants emerged this year without the diagnostic band. However, as the plants flower, this band is once again becoming evident.

The more familiar P. cortusoides has for some reason proved far more vigorous at the Moorbank Botanic Garden. These plants only germinated a year ago!

Another plant that has done extraordinarily well in a trough at Moorbank is the Pyrenean mossy saxifrage S. intricata, also often called (invalidly) S. nervosa. At home I grow this in a pot in the alpine house and plants in the garden have largely disappeared. It is not often seen in gardens, but I think it is very worthwhile and has lovely fresh green filigree foliage when not in flower.

Another plant in the same trough is a propagation of the Daphne x hendersonii clone I collected cuttings of in 2003 from the Nota Pass and which I call 'Nota Pink'. Here it is growing through another introduction, this time from the summit of Smolikas, the second highest mountain in Greece, the only locality for Aubrieta glabrescens, collected by the MESE AGS Expedition in 1999.

Another MESE introduction was the good garden plant called Silene atropurpurea, or Lychnis viscaria subsp. atropurpurea, depending on your taxonomy. Here it is growing with the excellent late narcissus 'Hawera', a good subject for troughs but possibly not in this rather sickly combination!

Finally, the Cretan Tulipa saxatilis flourishes and flowers well on this dry sunny bank. It is a poor flowerer here at Hexham, but the warmer drier air of the city probably suits it.

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